U.S. patent number 5,338,587 [Application Number 08/175,661] was granted by the patent office on 1994-08-16 for electrographic methods.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Dennis Abramsohn, Santokh S. Badesha, Louis D. Fratangelo, George J. Heeks, Arnold W. Henry, Joseph Mammino, David H. Pan.
United States Patent |
5,338,587 |
Mammino , et al. |
August 16, 1994 |
Electrographic methods
Abstract
An electrographic imaging member comprising a supporting
substrate and an outer layer of a volume grafted fluoroelastomer
comprised of a substantially uniform integral interpenetrating or
crosslinked network of a polyorganosiloxane grafted
fluoroelastomer.
Inventors: |
Mammino; Joseph (Penfield,
NY), Abramsohn; Dennis (Pittsford, NY), Heeks; George
J. (Rochester, NY), Henry; Arnold W. (Pittsford, NY),
Fratangelo; Louis D. (Fairport, NY), Pan; David H.
(Rochester, NY), Badesha; Santokh S. (Pittsford, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
21989223 |
Appl.
No.: |
08/175,661 |
Filed: |
December 30, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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54172 |
Apr 30, 1993 |
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Current U.S.
Class: |
430/53; 347/129;
347/154; 399/222; 428/35.8; 428/36.9; 428/421; 428/447; 428/450;
428/451; 428/457; 428/461 |
Current CPC
Class: |
G03G
5/14726 (20130101); G03G 5/14773 (20130101); G03G
5/14791 (20130101); G03G 13/22 (20130101); Y10T
428/31663 (20150401); Y10T 428/3154 (20150401); Y10T
428/31678 (20150401); Y10T 428/31692 (20150401); Y10T
428/31667 (20150401); Y10T 428/139 (20150115); Y10T
428/1355 (20150115) |
Current International
Class: |
G03G
13/00 (20060101); G03G 13/22 (20060101); G03G
5/147 (20060101); G05G 013/22 () |
Field of
Search: |
;430/48,126 ;355/211
;346/153.1 ;428/35.7,35.8,36.9,421,447,450,451,457,461 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Encyclopedia of Polymer Science and Engineering, vol. 8, 1987,
"Interpenetrating Polymer Networks", pp. 279-284, 294-295, 329-337.
.
Henry, Arnold W. et al. "Improving Release Performance of Viton
Fuser Rolls", Xerox Disclosure Journal, vol. 9, #1, Jan./Feb. 1984,
p. 43. .
Ferguson, Robert M., et al., "Viton/RTV Silicone Fuser Release
Overcoating," Xerox Disclosure Journal, vol. 11, #5, Sep./Oct.
1986, p. 207..
|
Primary Examiner: Ryan; Patrick J.
Assistant Examiner: Macholl; Marie R.
Attorney, Agent or Firm: Haack; John L.
Parent Case Text
This is a continuation of application Ser. No. 054,172, filed Apr.
30, 1993, now abandoned.
Claims
What is claimed is:
1. An electrographic imaging method comprising:
(a) providing an electroreceptor imaging member comprising: a
supporting substrate, a conductive ground plane, an optional
blocking barrier layer, an optional adhesive layer, and an outer
charge retentive layer comprising a volume grafted elastomer which
is a substantially uniform integral interpenetrating and
crosslinked network of a hybrid composition comprising a
polyorganosiloxane grafted fluoroelastomer;
(b) depositing a uniform electrostatic charge on the imaging member
or discharging a receiving member to a low or uniform voltage;
(c) creating an electrostatic latent image by imagewise deposition
of charged particles on the imaging member;
(d) developing the electrostatic latent image with
electrostatically attractable marking particles to form a toner
image using dry or liquid developer;
(e) transferring the toner image to the receiving member;
(f) optionally cleaning; and
(g) optionally repeating the charging, image writing, developing,
transferring, and cleaning steps.
2. The method of claim 1, wherein said fluoroelastomer is selected
from the group consisting of
poly(vinylidenefluoride-hexafluoropropylene) and poly(vinylidene
fluoride-hexafluoropropylene-tetrafluoroethylene).
3. The method of claim 1, wherein said polyorganosiloxane is
terminally functionalized and has the formula: ##STR4## where R is
independently an alkyl or alkenyl with from about 1 to 20 carbon
atoms or an aryl group with from about 6 to about 20 carbon atoms
wherein said aryl group may be substituted with an amino, hydroxy,
mercapto or an alkyl or alkenyl group with from about 1 to 18
carbon atoms, the functional group A is an alkene or alkyne with
from about 2 to 8 carbon atoms or an alkene or alkyne substituted
with an alkyl group with from about 1 to 18 carbon atoms or
substituted with an aryl group with from about 6 to 20 carbon atoms
and n is a number from about 2 to about 350 and represents the
number of disubstituted siloxane monomeric segments.
4. The method of claim 1, wherein the outer layer is from about 6
to about 200 micrometers thick.
5. The method of claim 1, wherein the supporting substrate is a
cylindrical sleeve.
6. The method of claim 1 wherein the supporting substrate is a
drum, endless belt or drum-belt hybrid.
7. The method of claim 1 wherein the imaging member further
comprises an intermediate conductive elastomer layer.
8. The method of claim 1 wherein said substrate is a conductive
metal selected from the group consisting of stainless steel, nickel
and aluminum or has a conductive layer applied thereto.
9. The method of claim 1 wherein said member charges capacitively
to at least 500 volts.
10. The method of claim 1 wherein the electrostatic charge on said
member decays less than about 20%.
Description
CROSS REFERENCE TO RELATED APPLICATIONS AND PATENTS
Attention is directed to the following copending applications
commonly assigned to the assignee of the present application, U.S.
application Ser. No. 08/035,023; U.S. application Ser. No.
07/815,215 now U.S. Pat. No. 5,266,431; U.S. application Ser. No.
07/887,943, now U.S. Pat. No. 5,257,045 ; U.S. application Ser. No.
08/044,870, filed Apr. 8, 1993; and U.S. application Ser. No.
08/044,860, filed Apr. 8, 1993.
Attention is also directed to commonly assigned U.S. Pat. No.
5,166,031, issued Nov. 24, 1992, entitled "Materials Package for
Fabrication of Fusing Components" and U.S. Pat. No. 5,141,788,
issued Aug.25, 1992, entitled "Fuser Member".
BACKGROUND OF THE INVENTION
This invention relates in general to electrography and, in
particular, to hybrid compounds, thin films and processes for
preparing and using the hybrid compounds and thin films in, for
example, preparing dielectric electroreceptor devices for use with
liquid ink development systems. In fabricating electrographic
imaging members, there is a need for materials which can be easily
prepared and which have a high level of mechanical stability and
solvent resistance. There are known a number of methods and
materials for forming electrographic imaging members, for example,
the aforementioned copending application U.S. application Ser. No.
07/815,215 filed Dec. 31, 1991. Illustrated in the copending
applications are devices having blocking layers which layers are
required for the devices to be effective.
In electrography, an electrostatic latent image is formed on a
dielectric imaging layer (electroreceptor) by various techniques
such as by an ion stream (ionography), stylus, shaped electrode,
and the like. Development of the electrostatic latent image may be
effected by the application of certain electrostatically charged
marking particles in either dry form or dispersed in liquid
media.
A hybrid composition or volume grafted elastomer comprising a
fluoroelastomer and a polyorganosiloxane that forms an integral
interpenetrating network has been disclosed in the aforementioned
commonly assigned U.S. Pat. No. 5,166,031. The volume graft
composition was used in fabricating a thermal fusing member for
use, for example, in fusing electrographic toner images.
Fluoroelastomers, such as VITON.RTM., may be coated directly onto
metallic substrates such as aluminum, steel or other suitable
ground planes to form dielectric receivers. When these
fluoroelastomer coated ground plane devices are corona charged by
known means, the devices exhibit high charge injection rates which
results in noncapacitive charging thereby causing high charge decay
rates and low development potentials. These results render
fluoroelastomer coated devices undesirable from a charging
perspective. However, fluoroelastomers possess desirable mechanical
properties, for example, durability, flexibility, solvent
resistance, and the like, which make them particularly attractive
for use in electroreceptor devices. The aforementioned high charge
injection rates can be controlled and lowered by applying a
blocking layer at an interface formed between the ground plane and
the fluoroelastomer. However, the application of the blocking layer
requires an additional coating step and additional drying and
curing time which may reduce yields and unnecessarily inflates
manufacturing costs.
There continues to be a need for improved fluoroelastomers or
hybrid compositions which embody both desired mechanical properties
and low charge injection rate properties and which fluoroelastomers
or hybrid compositions may be directly applied to a ground plane
metallic substrate in a single step without requiring the
application of an intermediate blocking layer at the interface
between the ground plane and the dielectric fluoroelastomer layer
in a separate step. There is a continuing need for electroreceptor
devices that are: convenient to prepare, economic, environmentally
acceptable, mechanically stable and highly durable, having low
charge injection and high capacitive charging properties.
SUMMARY OF THE INVENTION
In an object of the present invention, the electrographic imaging
member has a receiving layer or an outer layer comprised of a
volume grafted elastomer which is a substantially uniform integral
interpenetrating network of a hybrid composition of a
fluoroelastomer and a polyorganosiloxane, where the volume graft is
formed by dehydrofluorination of said fluoroelastomer by a
dehydrofluorinating agent, followed by a free radical addition or
polymerization reaction by the addition of an alkene or alkyne
functionally terminated polyorganosiloxane and a polymerization
initiator.
In another object of the present invention, the fluoroelastomer is
selected from the group consisting of poly(vinylidene
fluoride-hexafluoropropylene) and
poly(vinylidene-hexafluoropropylene-tetrafluoroethylene).
In a further aspect of the present invention, the
polyorganosiloxane has the formula: ##STR1## where R is
independently an alkyl, alkenyl or aryl with from about 1 to 20
carbon atoms or an aryl group substituted with an amino, hydroxy,
mercapto or alkyl or alkenyl group having less than 20 carbon
atoms. The functional group A, is independently an alkene or alkyne
with from about 2 to about 8 carbon atoms or an alkene or alkyne
substituted with an alkyl or aryl group with from about 1 to about
20 carbon atoms and n is a number representing siloxane monomeric
units and is about 2 to about 350.
In accordance with another object of the present invention, a long
life electrographic imaging member together with a process for
making the electrographic imaging member which does not require a
prior deposition or application of a blocking layer prior to the
deposition of the dielectric layer.
In yet another object of the present invention, the
dehydrofluorinating agent is selected from the group consisting of
primary, secondary and tertiary aliphatic and aromatic amines where
the aliphatic and aromatic groups have from about 2 to about 15
carbon atoms.
In still yet another object of the present invention the
dehydrofluorinating agent is a primary aliphatic amine such as an
alkyl amine having up to 20 carbon atoms.
Another object of the present invention provides free radical
polymerization initiators selected from the group consisting of
aliphatic and aromatic peroxides and azo compounds, with benzoyl
peroxide and azoisobutyronitrile free radical initiators being
preferred.
In a further object of the present invention, a supporting
substrate is a cylindrical sleeve, drum, endless belt or drum-belt
hybrid, and the like, having an outer coating layer of volume
grafted fluoroelastomer from 6 to about 200 micrometers thick.
Another object of the present invention provides for an
electrographic imaging member which includes an optional
intermediate elastomer layer such as a silicone or fluoroelastomer
layer and the volume grafted fluoroelastomer layer as an
overcoating.
In another object of the present invention is provided a method of
making an electrographic imaging member having a supporting
substrate and a volume graft charge retentive layer comprising, in
embodiments, applying a solution of the volume graft to the
supporting substrate and forming a coating layer thereon to form a
uniform durable outer layer on the substrate comprised of the
volume grafted fluoroelastomer material.
In still yet another object of the present invention is provided an
electrographic imaging member that may be used as dielectric
receiver with dry or liquid developer systems.
It is another object of the present invention to provide a
substrate having a bulk conductivity of less than or equal 10.sup.8
ohm/cm and has a conduction coating applied thereto as a ground
plane.
Another object of the present invention is to provide a substrate
having mechanical and thermal properties that allows pressure
transfer of toner images to a receiver sheet, preferably with
heat.
The foregoing objects are accomplished in accordance with this
invention in embodiments by providing an electrographic imaging
member comprising a supporting substrate and an outer layer of a
volume grafted elastomer which is a substantially uniform integral
interpenetrating network of a hybrid composition comprising a
fluoroelastomer and a polyorganosiloxane, said volume graft having
been formed by: dehydrofluorination of said fluoroelastomer by a
dehydrofluorinating agent; free radical grafting or addition of an
alkene or alkyne functionally terminated polyorganosiloxane and a
free radical initiator to the fluoroelastomer; and subsequent
curative crosslinking of the siloxane grafted fluoroelastomer
product.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are QV curves which show averaged values of measured
voltage versus charge cycles for a comparative control device and a
representative Example device measured at, for example, 0.5 seconds
after charging, respectively, of the present invention.
FIG. 1 shows representative charging at 26 nanocoloumbs/cm.sup.2
for each cycle for 25 cycles for control or comparative device
fabricated from VITON only as described in COMPARATIVE EXAMPLE
I.
FIG. 2 shows representative charging at 26 nanocoloumbs/cm.sup.2
for each cycle for 25 cycles for a device fabricated from volume
grafted VITON of EXAMPLE II. The control device of FIG. 1 reaches a
level of about 200 volts where all charges deposited during a 1
second cycle are lost due to a charge decay mechanism. The sample
device of FIG. 2 prepared in EXAMPLE II charges more capacitively,
to over 500 volts and retains most of the charge with little
decay.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to the application of a hybrid
composition of a fluoroelastomer, for example, VITON.RTM. and a
polyorganosiloxane which is referred to hereafter a "volume graft"
for use as a dielectric receiver. The hybrid composition may be
prepared by chemically bonding, for example, an oligomeric or
polymeric vinyl terminated dimethyl siloxane to VITON.RTM. by the
dehydrohalogenation reaction and free radical addition followed by
curative crosslinking of the siloxane grafted fluoroelastomer. The
hybrid volume grafted fluoroelastomers of the present invention
have excellent mechanical, thermal and physical properties in that
these hybrid materials typically have a long wearing life, for
example, imaging devices prepared according to the present
invention may be used for in excess of 5,000,000 imaging cycles,
and maintain toughness and strength in either a dry or liquid
developer environments. Imaging members of the present invention
may be employed in an electrographic imaging process, particularly
for high speed ionographic and liquid immersion development color
printing processes.
Use of the term "volume graft" is intended to define in embodiments
a hybrid layer of polyorganosiloxane which is both grafted or
covalently bonded to a fluoroelastomer and which grafted material
is also cross linked. The term covalently bonded is intended to
define the chemical bonding between a polymer backbone or chain
carbon atom of the fluoroelastomer and a functionally reactive atom
or site of the polyorganosiloxane. These bonds could be C--C, C--O,
C--N, C--Si, and the like, depending upon the functionality
selected. In the present invention a C--C linkage between the
polyorganosiloxane and the fluoroelastomer is preferred for
mechanical and structural integrity and for ease and convenience of
preparation. By the term volume graft, it is intended to define a
substantially uniform integral interpenetrating network of a hybrid
composition, wherein both the structure and the composition of the
fluoroelastomer and polyorganosiloxane are substantially uniform
when taken through different or random sections or slices of the
electrographic member, that is, homogeneous.
The term hybrid composition in embodiments is intended to define a
volume grafted composition which is comprised of randomly siloxane
grafted fluoroelastomer and randomly intermolecularly cross linked
siloxane grafted fluoroelastomers.
The term interpenetrating network in embodiments is intended to
define the addition polymerization matrix where siloxane grafted
fluoroelastomer polymer strands are intertwined and cross linked
with one another.
Electroreceptor imaging members are well known in the art.
Electroreceptor imaging members may be prepared by various suitable
techniques. Typically, a flexible or rigid substrate is provided
having an electrically conductive surface which may be the same or
differ from the substrate. A charge retentive layer is then applied
to the electrically conductive surface. A charge blocking layer may
optionally be applied to the electrically conductive surface prior
to the application of the charge retentive layer. If desired, an
adhesive layer may be utilized between the charge blocking layer
and the charge retentive dielectric layer.
The substrate may comprise numerous suitable materials having the
required mechanical and thermal properties. Accordingly, the
substrate may comprise a layer of an electrically nonconductive or
conductive material such as an inorganic or an organic composition.
Typical conductive substrates are stainless steel, nickel,
aluminum, copper, brass, and the like. As electrically
nonconducting materials there may be employed various resins known
for this purpose including: liquid crystal polymers, phenolics,
polyphenylene ether alloys, polyphenylene oxide alloys,
poly(amide-imides), polyarylates, polyarylsulfone,
polybenzimidazole, polyetheretherketone, polyetherimide,
polyetherketone, polyesters, polyimides, polyphenylene sulfide,
polysulfones, polycarbonates, polyamides, polyurethanes, and the
like, which may be rigid or flexible. The electrically insulating
or conductive substrate may be in the form of an endless flexible
belt, a web, a rigid cylinder, a sheet, a sleeve, a belt-drum
hybrid, and the like.
The thickness of the substrate layer depends on numerous factors,
including strength desired and economical considerations. Thus,
this layer for a flexible belt may be of substantial thickness, for
example, about 125 micrometers, or of minimum thickness less than
50 micrometers, provided there are no adverse effects on the final
electroreceptor device.
The electrically conductive layer, which may be the same or
different from the substrate depending upon the device structure
and performance desired, may vary in thickness over substantially
wide ranges depending, for example, on the degree of flexibility
desired for the electroreceptor member. Accordingly, for a flexible
imaging device, the thickness of the conductive layer may be
between about 20 Angstrom units to greater than about 1,000
Angstrom units, and more preferably from about 100 Angstrom units
to about 750 Angstrom units for an optimum combination of
electrical conductivity and flexibility. The conductive layer may
be an electrically conductive metal layer formed, for example, on
the flexible substrate by any suitable coating technique, such as a
vacuum depositing technique. Typical metals include aluminum,
zirconium, niobium, tantalum, vanadium and hafnium, titanium,
nickel, stainless steel, chromium, tungsten, molybdenum, and the
like. In general, a continuous metal film can be attained on a
suitable substrate, for example, a polyester web substrate such as
MYLAR.RTM. available from E. I. du Pont de Nemours & Co., with
magnetron sputtering. Alternatively, the conductive layer may be
prepared by dispersing conductive metal flakes or particles, as
suitably conductive pigment particles in a suitable binder
resin.
If desired, an alloy of suitable metals may be deposited on the
substrate. Typical metal alloys may contain two or more metals such
as zirconium, niobium, tantalum, vanadium and hafnium, titanium,
nickel, stainless steel, chromium, tungsten, molybdenum, and the
like, and mixtures thereof. A typical electrical conductivity for
conductive layers for electroreceptor imaging members in slow speed
devices is about 10.sup.5 ohms/square.
After formation of an electrically conductive surface, an optional
charge blocking layer or barrier layer may be applied thereto.
Generally, electron blocking layers for positively charged
electroreceptors prevent holes from the imaging surface from
migrating toward the conductive layer. Any suitable blocking layer
capable of forming an electronic barrier to charge injection at the
interface of the dielectric layer and the conductive layer may be
utilized. The blocking layer may be nitrogen containing siloxanes
or nitrogen containing titanium compounds such as trimethoxysilyl
propylene diamine, hydrolyzed trimethoxysilyl propyl ethylene
diamine, N-beta-(aminoethyl) gamma-amino-propyl trimethoxy silane,
isopropyl 4-aminobenzene sulfonyl, di(dodecylbenzene sulfonyl)
titanate, isopropyl di(4-aminobenzoyl)isostearoyl titanate,
isopropyl tri(N-ethylamino-ethylamino)titanate, isopropyl
trianthranil titanate, isopropyl
tri(N,N-dimethyl-ethylamino)titanate, titanium-4-amino benzene
sulfonate oxyacetate, titanium 4-aminobenzoate isostearate
oxyacetate, [H.sub.2 N(CH.sub.2).sub.4 ]CH.sub.3
Si(OCH.sub.3).sub.2, (gamma-aminobutyl) methyl diethoxysilane, and
[H.sub.2 N(CH.sub.2).sub.3 ]CH.sub.3 Si(OCH.sub.3).sub.2
(gamma-aminopropyl) methyl diethoxysilane, as disclosed in (U.S.
application Ser. Nos. 4,338,387, 4,286,033 and 4,291,110). A
preferred blocking layer comprises a reaction product between a
hydrolyzed silane and the oxidized surface of a metal ground plane
layer. The blocking layer may be applied by any suitable
conventional technique such as spraying, dip coating, draw bar
coating, gravure coating, silk screening, air knife coating,
reverse roll coating, vacuum deposition, chemical treatment, and
the like. The blocking layer should be continuous and have a
thickness of less than about 0.2 micrometer because greater
thicknesses may lead to undesirably higher voltages for the
dielectric layer of the electrophotoreceptor. Drying of the
deposited coating may be effected by any suitable conventional
technique such as oven drying, infrared radiation drying, air
drying, and the like.
An optional adhesive layer may be applied to the blocking layer or
conductive layer. Any suitable adhesive layer well known in the art
may be utilized. Typical adhesive layer materials include, for
example, polyesters, duPont 49,000 (available from E. I. DuPont de
Nemours and Company), Vitel PE100 (available from Goodyear Tire
& Rubber), polyurethanes, and the like. Satisfactory results
may be achieved with adhesive layer thickness between about 0.05
micrometer (500 Angstroms) and about 0.3 micrometer (3,000
Angstroms). Conventional techniques for applying an adhesive layer
coating mixture to the charge blocking layer include spraying, dip
coating, roll coating, wire wound rod coating, gravure coating,
Bird applicator coating, and the like. Drying of the deposited
coating may be effected by any suitable conventional technique such
as oven drying, infrared radiation drying, air drying, and the
like. In some cases, the charge blocking layer and the adhesive
layer may be the same material.
Any suitable and conventional technique may be utilized to mix and
thereafter apply the latent volume graft layer coating mixture to
form the charge retentive or dielectric layer. By use of the term
"latent volume graft layer" is meant that the mixture applied to
form the dielectric layer contains a siloxane grafted
fluoroelastomer and curative crosslinking system which system is
activated, with for example, with heating in an oven, after coating
to produce the desired crosslinked siloxane grafted fluoroelastomer
or volume graft layer. Typical application techniques include
spraying, dip coating, roll coating, wire wound rod coating, and
the like. Drying of the deposited coating may be effected by any
suitable conventional technique such as oven drying, infrared
radiation drying, air drying, and the like.
The volume grafting according to the present invention is performed
in three distinct reactive steps, the first involves the
dehydrofluorination of the fluoroelastomer preferably using an
amine or an aminosilicone compound. During this step hydrofluoric
acid is eliminated from the fluoroelastomer polymer backbone and
generates unsaturation, carbon to carbon double bonds, on the
fluoroelastomer polymer chain or backbone. The second step is the
free radical peroxide induced addition of the alkene or alkyne
terminated polyorganosiloxane to the carbon to carbon double bonds
of the dehydrofluorinated fluoroelastomer as summarized, for
example, in the accompanying scheme. The subscripts x and y
represent fluorinated and dehydrofluorinated, respectively,
monomeric units within the fluoroelastomer, base represents an
aforementioned dehydrofluorinating agent, and CH.sub.2
.dbd.CH--(SiOR.sub.2).sub.n --CH.dbd.CH.sub.2 represents, for
example, in embodiments, a suitable alkene functionalized
polyorganosiloxane grafting component where n is defined herein.
The product shown in the reaction scheme may react further via a
free radical processes to form higher molecular weight crosslinked
or extended structures depending on the conditions used and
reactant stoichiometry selected. The third step comprises a
curative process wherein the siloxane grafted fluoroelastomer is
intermolecularly crosslinked to form the desired interpenetrating
network or volume graft layer. ##STR2##
The fluoroelastomers that are useful in the practice of the present
invention are described in detail in U.S. Pat. No. 4,257,699 to
Lentz, as well as those described in commonly assigned U.S. Pat.
No. 5,061,965. As described therein these fluoroelastomers,
particularly from the class of copolymers and terpolymers of
vinylidenefluoride, hexafluoropropylene and tetrafluoroethylene,
known commercially under various designations as VITON A, VITON E,
VITON E60C, VITON E430, VITON 910, VITON GH and VITON GF. Other
commercially available materials include FLUOREL 2170, FLUOREL
2174, FLUOREL 2176, FLUOREL 2177 and FLUOREL LVS 76. Additional
commercially available materials include AFLAS a
poly(propylene-tetrafluoroethylene), FLUOREL II (LII900) a
poly(propylene-tetrafluoroethylene-vinylidenefluoride) both also
available from 3M Company, and the TECNOFLONS identified as
FOR-60KIR, FOR-LHF, NM, FOR-THF, FOR-TFS, TH, TN505 available from
Montedison Specialty Chemical Co. Typically, these fluoroelastomers
are cured with a nucleophilic addition curing system, such as a
bisphenol crosslinking agent with an accelerator as described in
further detail in the above referenced '699 Lentz Patent. A
preferred curing system is a nucleophilic system with a bisphenol
cross linking agent to generate a covalently cross-linked network
polymer formed by the application of heat following grafting of the
fluoroelastomer copolymer. The nucleophilic curing system may also
include an organophosphonium salt, and the like, accelerator. Some
of the commercially available fluoroelastomer polymers which can be
cured with the nucleophilic system are VITON E 60C, VITON B 910,
VITON E 430, VITON A, VITON B, VITON GF.
In a particularly preferred embodiment, the fluoroelastomer is one
having a relatively low quantity of vinylidenefluoride, such as in
VITON GF. The VITON GF has 35 mole percent vinylidenefluoride, 34
percent hexafluoropropylene and 29 mole percent tetrafluoroethylene
with 2 percent cure site monomer. It may generally be cured with a
conventional aliphatic peroxide curing agent such as lauryl
peroxide, and the like, as described herein.
The polyorganosiloxane having functionality according to the
present invention has the formula: ##STR3## where R is
independently an alkyl, alkenyl or aryl with from 1 to about 20
carbon atoms or an aryl group substituted with an amino, hydroxy,
mercapto or an alkyl or alkenyl group with from 1 to about 20
carbon atoms. The functional group A, is independently an alkene or
alkyne group having about 2 to about 8 carbon atoms or an alkene or
alkyne substituted with an alkyl or aryl group with from 1 to about
20 carbon atoms and n is a number and represents siloxane monomer
units and is of from about 2 to about 350. In the above formula,
typical R groups include methyl, ethyl, propyl, octyl, vinyl,
allylic crotnyl, phenyl, naphthyl and phenanthryl and typical
substituted aryl groups are substituted in the ortho, meta or para
positions with lower alkyl groups having less than about 15 carbon
atoms. Furthermore, in a preferred embodiment n is between about 60
and about 80 to provide a sufficient number of reactive groups to
graft onto the fluoroelastomer. Typical alkene and alkenyl
functional groups include vinyl, acrylic, crotonic and acetylenic
which may typically be substituted with methyl, propyl, butyl,
benzyl, tolyl groups, and the like.
The dehydrofluorinating agent which attacks the fluoroelastomer
thereby generating unsaturation is selected from the group of
strongly basic agents such as peroxides, hydrides, bases, oxides,
and the like. Preferred dehydrofluorinating agents are selected
from the group consisting of primary, secondary and tertiary,
aliphatic and aromatic amines, where the aliphatic and aromatic
groups with from 2 to about 15 carbon atoms. The group also
includes aliphatic and aromatic diamines and triamines with from
about 2 to about 15 carbon atoms where the aromatic groups may be
benzene, toluene, naphthalene, anthracene, and the like. It is
generally preferred for the aromatic diamines and triamines that
the aromatic group be substituted in the ortho, meta or para
positions. Typical substituents include lower alkylamino groups
such as ethylamino, propylamino and butylamino with propylamino
being preferred. Specific amino silane dehydrofluorinating agents
include N-(2 aminoethyl-3-aminopropyl)-trimethoxy silane,
3-(N-styrylmethyl-2-aminoethylamino) propyltrimethoxy silane
hydrochloride and (aminoethylamino methyl) phenethyltrimethoxy
silane.
The dehydrofluorinating agent generates double bonds by
dehydrofluorination of the fluoroelastomer compound so that when
the terminally unsaturated polyorganosiloxane is added with the
initiator, the addition or polymerization of the siloxane on the
fluoroelastomer is initiated. Typical free radical polymerization
initiators for this purpose are benzoyl peroxide,
azoisobutyronitrile (AIBN), and the like.
Other adjuvants and fillers may be incorporated in the hybrid
siloxane elastomer in accordance with the present invention as long
as they do not affect the integrity of the volume grafted
fluoroelastomer. Such fillers normally encountered in the
compounding of elastomers include coloring agents, reinforcing
fillers, crosslinking agents, processing aids, accelerators and
polymerization initiators. Following coating of the latent volume
graft on to the substrate, it is subjected to a stepwise curing
process wherein, for example, heating is for two hours at
93.degree. C. followed by 2 hours at 149.degree. C. followed by 2
hours at 177.degree. C. followed by 2 hours at 208.degree. C. and
16 hours at 232.degree. C.
The substrate for the electroreceptor imaging member according to
the present invention may be of any suitable material. In one
instance, it takes the form of a cylindrical tube of aluminum,
steel or certain plastic materials chosen to maintain rigidity,
structural integrity, as well as being capable of having a silicone
elastomer coated thereon and adhered firmly thereto. Typically, the
electroreceptor imaging member substrates may be made by injection,
blow, compression or transfer molding, or they may be extruded. In
a typical procedure the substrate which may be a steel cylinder is
degreased with a solvent and cleaned with an abrasive cleaner prior
to being primed with a primer such as Dow Corning 1200 which may be
sprayed, brushed or dipped followed by air drying under ambient
conditions for thirty minutes and then baked at 150.degree. C. for
30 minutes. A silicone elastomer or similar intermediate layer may
optionally be applied according to conventional techniques such as
injection molding and casting after which it is cured for up to 15
minutes and at 120.degree. to 180.degree. C. to provide a complete
cure without a significant post cure operation. The silicone
elastomer intermediate layer may be pigmented with carbon, metal
flakes, and the like, to achieve a resistivity of .ltoreq.10.sup.8
ohm/cm and have a Shore A durometer value of about 40 to 80 and a
thickness of about 12.5 micrometers to about 1,000 micrometers. The
intermediate curing operation should be substantially complete to
prevent debonding of the silicone elastomer from the substrate when
it is removed from the mold. Thereafter the surface of the silicone
elastomer is sanded to remove the mold release agent and it is
wiped clean with a solvent such as isopropyl alcohol to remove all
debris.
The outer layer of the electroreceptor imaging member is preferably
prepared by dissolving the ungrafted fluoroelastomer in a typical
solvent, such as methyl ethyl ketone (MEK), methyl isobutyl ketone
(MIBK), and the like, followed by stirring for 15 to 60 minutes at
45.degree. to 85.degree. C. after which the free radical initiator,
which is generally dissolved in an aromatic solvent such as
toluene, is added with continued stirring for 5 to 25 minutes.
Subsequently, the polyorganosiloxane is added with stirring for 30
minutes to 10 hours at a temperature of about 45.degree. to
85.degree. C. A curing package such as, VITON CURATIVE No. 50,
which incorporates an accelerator, (a quarternary phosphonium salt
or salts) and a crosslinking agent, bisphenol AF in a single
curative system is added in a 3 to 7 percent solution predissolved
in the fluoroelastomer compound. Optimally, the basic metal oxides
or hydroxides, such as MgO and Ca(OH).sub.2, can be added in
particulate form to the solution mixture. Providing the charge
retentive layer on the electroreceptor imaging member substrate is
most conveniently carried out by spraying, dipping, and the like, a
solution of the homogeneous suspension of the siloxane grafted
fluoroelastomer containing the curative system to a level of film
of about 6 to about 200 micrometers in thickness. This thickness
range is selected as providing a layer thin enough to minimize cost
of the device and thick enough to allow a reasonable wear life and
preferrable charging properties. While molding, extruding and
wrapping techniques are alternative means which may be used, a
preferred means is to spray successive applications of a solvent
solution. When the desired thickness of coating is obtained, the
coating is cured and thereby bonded to the substrate. A typical
stepwise curing process is heating for two hours at 93.degree. C.
followed by 2 hours at 149.degree. C. followed by 2 hours at
177.degree. C. followed by 2 hours at 208.degree. C. and 16 hours
at 232.degree. C.
In an alternative procedure, the solvent may be removed by
evaporation by known means, the residue rinsed with a hydrocarbon
solvent such as hexane to remove unwanted reactants, if any, and
the residue redissolved in the original solvent followed by the
addition of VITON CURATIVE No. 50 and subsequent formation of an
outer layer.
Other layers may also be used such as conventional electrically
conductive ground strip along one edge of the belt or drum in
contact with the conductive layer, blocking layer, or adhesive
layer to facilitate connection of the electrically conductive layer
of the electroreceptor to ground or to an electrical bias. Ground
strips are well known and usually comprise conductive particles
dispersed in a film forming binder.
Optionally, a protective overcoat layer may also be utilized to
enhance resistance to abrasion. In some cases an anti-curl back
coating may be applied to the side opposite the outer
electroreceptor layer to provide flatness and/or abrasion
resistance. These overcoating and anti-curl back coating layers are
well known in the art and may comprise thermoplastic organic
polymers or inorganic polymers that are electrically insulating or
slightly semi-conductive. Overcoatings are continuous and generally
have a thickness of less than about 10 micrometers.
The devices employing a hybrid charge retentive layer of the
present invention exhibit numerous advantages such as extremely
stable charge and operational life longevities. Moreover, high
stable charge and mechanical integrities are maintained during
extended cycling in a machine employing liquid development systems
comprised of, for example, hydrocarbon solvents.
The imaging member of the present invention may be employed in an
electrographic imaging process comprising:
(a) providing an electroreceptor imaging member comprising: a
supporting substrate, a conductive ground plane, an optional
blocking barrier layer, an optional adhesive layer, a charge
retentive layer comprising a volume grafted elastomer which is a
substantially uniform integral interpenetrating or crosslinked
network of a hybrid composition comprising a polyorganosiloxane
grafted fluoroelastomer;
(b) depositing a uniform electrostatic charge on the imaging member
or discharging the receiving member to a low or uniform
voltage;
(c) creating an electrostatic latent image by imagewise deposition
of charged particles on the imaging member;
(d) developing the electrostatic latent image with
electrostatically attractable marking particles to form a toner
image using dry or liquid developer;
(e) transferring the toner image to a receiving member;
(f) cleaning; and
(g) repeating the charging, image writing, developing,
transferring, and cleaning steps.
X-ray Photoelectron Spectroscopy (XPS) Characterization of the
Volume Grafted Layer.
The electrographic imaging members prepared in the present
invention may have the volume grafted fluoroelastomer layer
conveniently characterized using X-ray photoelectron spectroscopy
as described below.
1. Preparation of Surface - The volume grafted fluoroelastomer
layer prepared in EXAMPLE II was sequentially solvent extracted
with hexane or 90/10 hexane/methyl ethyl ketone mixed solvents 3 to
4 times to remove unreacted fluoroelastomer and siloxane.
2. XPS Characterization - The extracted layer remaining was then
examined with X-ray photoelectron spectroscopy which provides the
chemical composition of the topmost 5 to 10 nanometers of the layer
surface. The surface was then sliced two times and XPS analysis
indicated that polysiloxane is uniformly distributed throughout the
fluoroelastomer film.
The following Examples further define and describe ionographic
imaging members prepared by the present invention and illustrate
preferred embodiment of the present invention. Unless otherwise
indicated, all parts and percentages are by weight. A comparative
Example is given.
EXAMPLE I
Preparation of Siloxane and VITON Volume Graft Material
A volume graft elastomer was prepared by dissolving 250 grams of
VITON GF.TM. in 2.5 liters of methylethyl ketone (MEK) by stirring
at room temperature. This was performed in a 4 liter plastic bottle
using a moving base shaker for about one hour to two hours to
accomplish the dissolution depending upon the speed of the shaker.
The above solution is then transferred to a 5 liter Erlenmyer flask
and 25 milliliters of the amine dehydrofluorinating agent,
3-(N-styrylmethyl-2-aminoethylamino) propyltrimethoxysilane
hydrochloride (S-1590, available from Huls America Inc.,
Piscataway, N.J.) was added. The contents of the flask were then
stirred using a mechanical stirrer while maintaining the
temperature between 55.degree. and 60.degree. C. After stirring for
30 minutes, 50 milliliters of 100 centistoke vinyl terminated
polysiloxane (PS-441) also available from Huls America Inc., was
added and stirring was continued for another ten minutes. A
solution of 10 grams of benzoyl peroxide in a 100 milliliter
mixture of toluene and MEK (80:20) was then added. The stirring was
continued while heating the contents of the flask at about
55.degree. C. for another 2 hours. During this time, the color of
the solution turned light yellow, the solution was then poured into
an open tray. The tray was left in a fume hood for 16 hours. The
resulting yellow rubbery mass remaining after air evaporation of
the solvent was then cut into small pieces with a scissor. This
material was then extracted extensively and repeatedly with 1,500
milliliters (three 500 milliliter portions) of n-hexane to remove
unreacted siloxane.
Thereafter, 54.5 grams of the prepared silicone grafted
fluoroelastomer, together with 495 grams of methyl isobutyl ketone,
1.1 grams of magnesium oxide and 0.55 gram of calcium hydroxide
(CaOH).sub.2 were added to a jar containing ceramic balls followed
by roll milling for 17 to 24 hours until a fine, 3 to 5 microns in
diameter particle size of the fillers in dispersion was obtained.
Subsequently, 2.5 grams of DuPont VITON CURATIVE VC50.TM. catalyst
crosslinker in 22.5 parts of methyl ethyl ketone were added to the
above dispersion, shaken for about 15 minutes and the solids
content reduced to 5 to 7 percent by the addition of methyl
isobutyl ketone. Following hand mixing, the mixture was ready for
spray coating.
EXAMPLE II
Device Fabrication
The volume graft composition of Example I was coated onto a 2.2 mil
thick sheet of stainless steel. The sheet was abraided with
sandpaper, degreased using methylene chloride, scrubbed with an
abrasive cleaner, thoroughly washed with water and dried prior to
spray coating and then cured in an oven at 260.degree. C. for about
2 hours. The dried film thickness of the coating was 10.7
micrometers. The electroreceptor device produced does not contain a
blocking layer. It was observed that the resulting dielectric
coating had considerably better capacitive charging properties, and
a higher development potential then a control device prepared from
uncrosslinked or non-volume grafted VITON as described below in
Comparative Example I and as indicated in the figures. That is, the
device prepared from the volume graft composition of Example I
charged to higher levels (400 to 500 volts versus about 200 volts)
and maintained or stabilized voltage levels (about 400 volts versus
less than 50 volts after 30 cycles) to a greater extent than the
control device of Comparative Example I. XPS analysis indicated
that the polysiloxane compound was uniformly distributed throughout
the VITON fluoroelastomer matrix.
EXAMPLE III
The volume graft composition of Example I was coated onto stainless
steel sheets as described in Example II to produce a series of dry
film coatings of 12.5, 50 and 75 micrometers thickness. The
coatings were dried at 50.degree. C. for 16 hours and then at
200.degree. C. for about 24 hours. Each dielectric coating was
charged by an ionographic charging device of the type described in
the aforementioned U.S. application Ser. No. 07/887,943, to
generate an image pattern which was then developed using a magnetic
brush developer. The toner image was transferred to paper and
fused. The dielectric coating was cleaned of residual toner and
recharged to develop several more images. The devices with coatings
with 50 and 75 micrometers thick volume graft composition produced
images accceptable to a trained observer with dense solid areas and
sharp line and edge definition compared to the 12.5 micrometers
thick volume graft coating composition device which images were not
acceptable. XPS analysis indicated that the polysiloxane compound
was uniformly distributed throughout the VITON fluoroelastomer
matrix.
EXAMPLE IV
Device Fabrication
An imaging member was prepared as follows. An aluminum cylinder
core substrate was grit blasted and degreased with solvent, dried
and primed with an epoxy adhesive Thixon 300/301 over which a base
coat comprising part A of 100 parts VITON GF, 30 parts of N990
carbon black, 15 parts MAGLITE Y(MgO) in methyl isobutyl ketone
(MIBK) to a 15 percent solids mixture, and part B of 5 parts of
VITON CURATIVE VC50 and 28.3 parts of MIBK. Part B was added to
part A and roll milled for 45 minutes, then sprayed onto the primed
core cylinder to a thickness of 150 micrometers after which the
member was desolvated at ambient conditions for two days followed
by a step cure of 2 hours at 38.degree. C., 4 hours at 77.degree.
C., 2 hours at 177.degree. C., and then the sprayed surface layer
was sanded to a thickness of 5.5 mils. Next 250 g of VITON GF was
dissolved in 2.5 liter of methylethyl ketone (MEK) by stirring at
room temperature. This is accomplished by using a four liter
plastic bottle and a moving base shaker. It takes approximately one
hour to two hours to accomplish the dissolution depending upon the
speed of the shaker. The above solution is then transferred to a 4
liter Erlenmyer flask and 25 ml of the amine dehydrofluorinating
agent N-(2-aminoethyl-3 aminopropyl)-trimethoxy silane (A0700,
available from Huls America Inc., Piscataway, N.J.) was added. The
contents of the flask were then stirred using a mechanical stirrer
while maintaining the temperature between 55.degree. and 60.degree.
C. After stirring for 30 minutes, 50 mL of vinyl terminated
polysiloxane (PS-441) was added and stirring continued for another
ten minutes. A solution of 10 grams of benzoyl peroxide in a 100 mL
mixture of toluene and MEK (80:20) was then added. The stirring was
continued while heating the contents of the flask around 55.degree.
C. for another 2 hours. During this time the color of the solution
turned light yellow. To this solution was added VITON CURATIVE No.
50 in a 3 to 7 percent solution. The outer layer of the
electroreceptor was spray coated to a thickness of 50 micrometers
using the above solution and cured according to Example II. When
the above electroreceptor is used in an imaging system, it has
proven to provide satisfactory imaging properties and performance.
X-ray photoelectron spectroscopy characterization was performed on
this imaging member as in Examples II and III with similar results;
a uniform distribution of the polysiloxane throughout the elastomer
film matrix was indicated.
COMPARATIVE EXAMPLE I
A control device was prepared in the same manner as the volume
graft device of EXAMPLE II with the exception that only VITON.RTM.
GF was used for the purpose of coating instead of volume grafted
siloxane VITON GF that was prepared in Example I. The resulting
device had a thickness of 13.7 micrometers.
The following procedure was used for testing each of the samples
produced in the Example II and Comparative Example I. Typical
results from this procedure for certain examples are depicted in
the FIGS. 1 and 2. Each sample was individually mounted on the
outside surface of an aluminum drum of about 3 inches in diameter.
The drum and sample were rotated at about one second per cycle
under a 5 cm long corotron wire mounted with the wire parallel to
the drum axis and controlled by a TREK model 610B to provide a
continuous fixed charge current level. Thus, during each cycle, the
sample was provided a fixed charge Q. Simultaneously, 6 non-contact
voltage probes, such as from a TREK model 565 electrostatic
voltmeter, were mounted radially to the drum at several angular
intervals at a common axial position to measure the surface
potential of the sample at various times after charging. This
procedure provides a voltage versus charge cycle and/or voltage
versus charge for each sample and thus provides the inverse Q-V
(charge versus voltage) characteristics relevant to electrical
performance.
The QV curves shown in FIGS. 1 and 2, indicate charging at 26
nanocoloumbs/cm.sup.2 each cycle for 25 cycles for devices
fabricated from a control VITON.RTM. as described in COMPARATIVE
EXAMPLE I and from the volume graft as prepared in EXAMPLE II of
the present invention. The control sample reaches a level of 200
volts where all charges deposited during a one second cycle are
lost due to charge decay mechanisms. That is the device of
Comparative Example I does not charge capacitively and losses or
leaks charge potential which retained charge is required for
efficient charging, system stability and wider imaging process
latitude. The volume graft prepared material of EXAMPLE II charges
much more capacitively to over 500 volts. The device of EXAMPLE II
charges capacitively, holds charge longer and thereby enables
improved electrographic imaging processes. The control device is
13.7 micrometers in thickness whereas the volume graft prepared
device is 10.7 micrometers thick.
All patents and copending applications referred to herein are
hereby specifically incorporated by reference herein in their
entirety.
While the invention has been described in detail with reference to
specific and preferred embodiments, it will be appreciated that
various modifications and variations will be apparent to the
artisan. All such modifications and embodiments as may readily
occur to one skilled in the art are intended to be within the scope
of the appended claims.
* * * * *